1. Field of the Invention
The invention relates to an apparatus treating liquid sewage.
2. Description of Prior Art
Individual homes or small population centers which do not have conventional sewage systems are typically served by what is termed "package plant" for the treatment of sewage. Typical of one process employed in such package plants is the contact-stabilization method.
The contact-stabilization method or process is comprised of four basic steps: contact, sedimentation, stabilization and digestion. Liquid sewage to be treated is introduced into a contact chamber or tank where it is mixed and aerated with sludge solids returned to a stabilization tank. The sewage typically remains in the contact tank for from 15 to 20 minutes during which time the raw sewage and sludge under go chemical and bacteriological changes which convert most of the solids in the sewage to a suspension of liquid and activated sludge floc. Following this contact, solid particles of sewage pass into a sedimentation tank chamber where the floc settles out of the liquid suspension and is directed back to the stabilization tank where such solids remain for a period of approximately 5 hours. The stabilization tank is also aerated and mixed.
Following the 5 hour period, a portion of the floc is returned as return sludge or return solids to the contact tank and the process is repeated. The heavier sludge solids settle into a digestion tank or chamber, generally located beneath the stabilization tank where it is aerobically digested. Periodically the nondigested organic particles are removed from the digester by mechanical suction means. Liquid remaining in the sedimentation tank after the floc has settled out is discharged from the system as a purified effluent. Chlorine or other purifying agents may be mixed with the effluent prior to its discharge from the package system.
In use the contact stabilization process for package plants has permitted high organic loadings for a compact and versatile package plant of unitary construction. However, the short period of 15 to 30 minutes when combined with the substantial peak loadings inherent in such package plants in the systems of isolated individual dwellings and small population centers has resulted in an unstable and unreliable treatment system. Additionally, a relatively short 5 hour stabilization period results in a high solids accumulation rate with an attendant solids disposal problem.
In addition to the problems of inadequate contact time and possible inadequate treatment during peak loadings, such plants typically utilize compressed air for the aeration of the sewage to be treated, and the air compressors required for such systems frequently require substantial maintenance in order to keep them in operable condition.
An object of this invention is to provide an improved apparatus for the treatment of liquid sewage. Other additional objectives will be apparent upon a reading of the entire specification, drawings and claims.